Abstract
Environmental odour samples are often comprised of complex mixtures of compounds with diverse chemical properties and key odorants can be present at concentration levels in the low ppb range. This complicates accurate odour evaluations as adsorption to the inner walls of sampling equipment may significantly alter the chemical composition of the sample, even when the adsorption capacity is low. In the present study, the significance of saturation effects in dynamic Olfactometry on the recovery of single compounds in the low ppb range and the impact on the chemical composition of odour samples typical for livestock houses is evaluated. The results are based on extensive measurements of three olfactometers obtained from accredited odour laboratories, i.e. a TO8, a glass-tube olfactometer and a dilution system based on a mass flow controller. The odorants include hydrogen sulphide, methanethiol, dimethyl sulphide, acetic acid, butanoic acid, propanoic acid, 3-methylbutanoic acid, 4-methylphenol, and trimethylamine. Furthermore, n-butanol, the reference gas according to the European standard, was included. All measurements were performed in real time with high sensitivity Proton Transfer Reaction Mass Spectrometry (PTR-MS). The results show that several key odorants, including 4-methylphenol, trimethylamine and some carboxylic acids, were affected by surface adsorption to an extent, which could likely alter the outcome of odour measurements. Hence, it is recommended to carefully consider olfactometer configuration and compound recovery for this type of odour samples.
